Many thermoplastic polymers such, for example, as the homo- and copolymers of methyl methacrylate, polyolefins, polystyrene and acrylonitrile-butadiene-stryene resins are hard and, in many instances, optically clear materials which are widely utilized for the preparation of a broad range of consumer and industrial articles. As normally prepared, these thermoplastic polymers will ignite and continue to burn upon exposure to flames or high temperatures. However, in many instances, particularly where they are being considered for use in building interiors or in applications requiring their prolonged exposure to high temperatures, it is highly desirable that such polymers should display fire or flame retardant properties so that they may either meet the standards set by various building codes or so that they may be safely employed in place of more costly materials.
Prior attempts to provide fire retardant, thermoplastic polymer compositions have involved the use of a variety of extraneous additives such, for example, as antimony oxides, halogenated paraffins, halogenated hydrccarbons and low molecular weight phosphate esters. However, the effective utilization of these and other additives has ordinarily required their presence in rather high concentrations which adversely affected the physical properties of the treated polymers. Thus, the inherent hardness and, in some instances, the clarity of the thermoplastic polymers were particularly prone to deterioration in the presence of the high concentrations of these additives which were necessary in order to achieve a self-extinguishing polymer composition.
It is, therefore, the prime object of this invention to provide fire retardant thermoplastic polymer compositions by the use of additives whose presence will not adversely affect the inherent physical properties such as hardness and, in some instances, the clarity of the thus modified polymers. It is a further object of this invention to provide a novel class of copolymers which are particularly useful, as additives, for preparing fire retardant, thermoplastic polymer compositions. Various other objects and advantages of this invention will be apparent from the disclosure thereof which follows hereinafter.